The present invention relates to an aerosol interface device that is particularly suited for therapy applications in which an aerosol fluid is inspired by the patient during each inhalation period.
One of the therapeutic modes of treatment for respiratory diseases is the administration of moisture and/or drugs via an aerosol. Several systems for generating aerosols suitable for respiratory therapy are available commercially. The interface between an aerosol generator and the patient involves several unique problems which are not wholly answered by currently available equipment. The subject invention discloses a new and efficient interface for use in the administration of aerosol therapy.
The basic problem confronting the aerosol generator-patient interface centers on the fact that the breathing patient is a cyclic (inhale-exhale) system while the generator functions best as a continuous flow system. The standard mist tent encloses the patient's head and upper body with an aerosol filled canopy to insure that a supply of concentrated aerosol is readily available for each inhalation cycle, but aerosol fallout over large areas plus excess aerosol output required to preclude carbon dioxide buildup within the enclosure results in aerosol waste and excess aerosol generating capacity requirements. The standard aerosol face tent (a large open top face mask) fails to economize aerosol because the flow of exhaled gases tends to sweep aerosol from the face tent to nullify any pre-inhalation accumulation.
The standard enclosed aerosol mask and the standard mouthpiece have the same problems as the face tent. If a high level of aerosol density is desired all of the standard interface systems require excessively high output flow from the aerosol generator in order to provide undiluted aerosol during peak inspiratory flow rates; the net result is a high level of aerosol waste during exhalation and during low inhale flow rates.
Some aerosol therapy systems attempt to get around the above problems by generating aerosol during inhalation only, but this presents a problem of coordination with the breathing cycle plus loss of effectiveness because most aerosol generators have a significant time lag between start of generation and arrival of aerosol at the patient. The standard aerosol interface systems are not satisfactory because they waste aerosol which may contain a very expensive drug, they require high generating capacity to achieve a desirable inhaled aerosol density, and they are uncontrolled in their rate of delivery to the patient's lung (a fact that can have serious consequences when potent drugs are involved).
An interface system which contains a volume to accumulate aerosol generated during exhalation and provides a double check valve arrangement to steer exhaled gases away from the accumulated aerosol and to direct inhaled gases toward the patient from the accumulator volume and source of aerosol generation, would seem to solve most of the above interface problems. Up until now the typical breathing flow steering valve designs involve a mechanical poppet and valve seat arrangement. Such valves are not satisfactory for aerosol flow control because of an inherent tendency for the movable valve to provide a small flow passage at low flow rates which becomes a means for elimination of the aerosol by coalescence while flowing through the small opening.
The advantages and distinctions of my invention over the prior art will become more clearly evident as the disclosure proceeds, and is obtained by utilizing an accumulator/airflow steering interface system which contains always open, nonrestrictive passageways.